Polymeric web shredding

ABSTRACT

A method and apparatus for the shredding of a polymeric web wherein the web is subdivided in two sequential steps, the first constituting a planar cut removing a segment having a serrated edge configuration and the second constituting a multiple cut transverse the segment.

United States Patent 1 [111 3,762,256 Frantz Oct. 2, 1973 [5 POLYMERIC WEB SHREDDING 2,798,550 7/1957 Kubodera 83/356 3,342,093 9/1967 Billingsley 83/906 X inventor. David Louis Frantz, Newark, Del. 3,353,754 11/1967 Hail-is et a1." 241/243 X 73 Assignee: E. I. du P de Nemours and 3,545,686 12/1970 Brown 241/243 X Company, Wilmington, Del. [22] Filed: Apr. 17, 1972 Primary ExaminerJ. M. Meister pp No: 244,717 Attorney-Harry J. McCauley [52] US. Cl 83/3563, 83/357, 83/402, {57] ABSTRACT 83/906, 241/190, 241/243 [51] 1111. C1 823d 25/00 A method and apparatus for the Shredding of a poly [58] Fleld 0158311211 83/355, 356, 356.1, meric web wherein the web is subdivided in two 83/3563 357? 241/158, quential steps, the first constituting a planar cut remov- 300-1 ing a segment having a serrated edge configuration and the second constituting a multiple cut transverse the [56] References Cited Segmem UNITED STATES PATENTS 1,131,230 3/1915 Giddings 241/243 6 Claims, 6 Drawing Figures 40 i 1/ r I 3 I 9 I 9 33 x l /1 I PATENTED 2375 3 752 256 snzn 1a; 3

PATENTED E 2 I 73 SHEET 3 BF 3 POLYMERIC WEB SHREDDING BRIEF SUMMARY OF THE INVENTION Generally, this invention comprises a two-step method for shredding a polymeric web comprising, in sequence, cutting a segment from the web having a regular serrated edge configuration, shifting the segment laterally a distance of substantially one half the serration pitch, rotating the segment approximately 90 from the position at which the segment is cut from the web and cutting the segment transversely at a multiplicity of points, together with apparatus for carrying out the method.

DRAWINGS In the drawings,

FIG. 1 is a side elevation view of a preferred embodiment of this invention looking in the direction of line 1l, FIG. 2,

FIG. 2 is a section taken along line 22, FIG. 1,

FIG. 3 is a perspective plan view looking generally outwards from the rotary cutter showing the two stationary sawtooth bed knives of the apparatus of FIGS. 1 and 2 and the polymeric cut-out segment guide means therebetween,

FIG. 4 is a perspective view of the rotary cutter of the apparatus of FIGS. 1 and 2,

FIG. 5 is a sectional view taken on line 5-5, FIG. 3, and

FIG. 6 is a diagrammatic representation taken on line 6-6, FIG. 2, of the successive positions assumed by each individual cut-out segment in transit between the two stationary sawtooth bed knives of the apparatus of FIGS. l-5, inclusive, in the course of shredder operation.

DETAILED DESCRIPTION The continuous manufacture of polymeric webs commonly involves, first, laying down the polymer as a cast, relatively thick, amorphous mass, which is thereafter oriented in first one direction and then another by a stretching operation, which not only imparts high strength but also progressively reduces the thickness to that of the final product. The film thereby produced is of uniform thin gage, permitting its slitting to mill roll size for sale to photographic film base, magnetic recording tape, and general packaging customers.

Web manufacture, as described, thus involves a progressively increasing rate of web advance from a very low velocity at the outset to a relatively high velocity of 100 ft./min. or more at product delivery. Inevitably, there is considerable waste material which must be speedily removed and recovered as salvage during both the initial start-up and any subsequent critical periods during which web breaks occur at any point in the process. Such waste is produced very quickly in large quantities, and it is imperative that it be removed from the manufacturing area as speedily as possible by diversion to high-speed shredders strategically located adjacent the manufacturing appartus, particularly at points where convenient waste take-off can be effected.

The shredder of this invention is intended for particularly heavy duty service in the chip reduction of extremely tough organic polymeric webs, such as unidirectionally oriented thermoplastic films of the type represented by polyesters and the like. These webs vary from heavy, unoriented, shatterable as-cast sheets at the outset of the process to bioriented, fracturable lightweight films as the final product and, of course, the shredder has to be capable of handling both extremes of waste input as well as all variations in between.

Another variable which has to be accommodated is web width continuity, ranging from unitary full width at one extreme to narrow edge remnants only at the other.

The shredding apparatus of this invention is an improvement on the design of U. S. Pat. No. 3,545,686, and provides two-stage size reduction of waste, which has proved to be essential for the high-speed disposal of the toughest polymeric webs presently produced by industry.

Referring to FIGS. 1 and 2, particularly, the shredder apparatus of this invention is mounted within a housing, denoted generally at 2, which is supported on a stationary frame denoted generally at 3, which is rein forced by stiffeners and brackets, not detailed, for strength and rigidity.

Housing 2 comprises an upper section, or cover, 4, which is bolted to a lower section 5, so that cover 4 can be removed for apparatus inspection and maintenance.

Section 5 is securely attached to a cross-frame 3a by hold-down bolts (not shown).

The left-hand wall of cover 4, as seen in FIG. 2, is apertured to provide a narrow entrance slot 6 for introduction of the web 40 to be shredded. Typically, the polymeric web 40 has a thickness in the range of 0.004 inches to 0.035 inch and a full width of 65 inch.

A retractable debris-retaining auxiliary, denoted generally at 7, hereinafter described in greater detail, is provided at the web entrance end of slot 6.

A cut-product draw-off collector funnel 12 is connected at its inlet end 11 in open communication with the lower end of section 5, and this is provided at its reduced end with an air-swept waste conveyor conduit 13. Conduit 13 is run to a waste storage bin at a remote location (not shown), and the flow circuit incorporates a conventional particulate material entrainment conveying blower (also not shown) which continuously draws a high velocity stream of air through slot 6, thence through housing 2 and out conduit 13, thereby removing shredded polymer as rapidly as it is formed, and avoiding clogging of housing 2.

Referring to FIGS. 2 and 4 particularly, a preferred embodiment of this invention comprises a powerdriven rotary cutter, denoted generally at l, which is provided on the periphery with at least one radially disposed edge-sharpened removable sawtooth knife 20 aligned substantially co-parallel with the longitudinal axis of the rotary cutter. Knife 20 interacts'successively with a first, or primary stationary sawtooth bed knife 8 and then with another, or secondary, stationary sawtooth bed knife 9. These bed knives are each provided with edge-sharpened sawtooth cutting elements functioning as cutters by interdigitation with the sawteeth of knive 20 during its rotation.

Preferably, to increase the shredding rate, the apparatus is provided with a multiplicity of rotary cutter knives 20 disposed equiangularly around the circumference of the rotor 1, six, separated at regular spacings of each, being detailed in FIG. 2.

Referring to FIG. 4, the central drum of rotary cutter l is cylindrically shaped and is provided with co-axial shaft extensions 14a, 14b which are journaled rotatably in heavy duty antifriction bearings 15a, 15b (FIG. 1)

secured to mounting pads on cross frame 3a. Shaft extension 14b is provided with a drive pulley 16, and the cutter is power-driven by a plurality of V-belts 17 engaging with the power delivery pulley 18a of drive motor 18. A bracket 19, bolted to frame 3, supports motor 18.

As seen in FIG. 4, the sawtooth knives 20 of rotary cutter I extend almost the full length of rotor 1, substantially coparallel with the rotor axis and are fixedly secured within longitudinal slots in the rotor by wedge bars 21 and threaded fasteners 21a. The rotor is cut away circumferentially, as denoted at 22, to provide clearance facilitating air flow through the housing 2.

As indicated by the rotational arrow in FIG. 2, rotary cutter 1 is driven counter-clockwise, so that the teeth of knives 20 interdigitate first with the teeth of bed knife 8 to effect the first, or primary, planar cut on the entering web 40 to be shredded. Each knife 20 sweep cuts away a lengthy segment 35 (FIG. 6) from the web, these segments having regularly serrated edge configurattions of zig-zag pattern adapting them to further processing.

It is important that primary bed knife 8 be mounted somewhat below the axis of cutter I (typically, about 30), so that the leading tips of the sawteeth of knives 20 first pierce and thereafter shear, or tear, the incoming web, as well as provide a self-feeding pull on the web.

Secondary bed knife 9 is disposed 90 or more counter-clockwise from primary bed knife 8, corresponding to approximately 70 peripheral expanse of cutter 1 in the construction of FIG. 2, to obtain controlled uniform lateral shifting of each and every segment 35 to effect uniform transverse multiple cutting of the segments 35 as the second and final step of the shredding process.

As shown in FIGS. 2 and 6, secondary bed knife 9 is supported in radial disposition with respect to rotary cutter l by a plurality of horizontal struts 23 secured to the inside wall of cross frame 3a. Bed knife 9 is retained in position by secure attachment within a clamp support 23a by machine screws (not shown) and is somewhat inclined toward primary bed knife 8, in this instance, at an angle of about 15, thereby providing more space at the opening 11 of collector funnel 12 for air-swept removal of web cuttings away from the shredding apparatus.

Referring to FIGS. 2, 3, and 6, the apparatus is provided with a plurality of arcuate guide members 10, which are vertically disposed thin metal strips extending across the cut piece removal portion of the inlet end 11 of draw-off funnel 12. Guide members are disposed with center lines accurately aligned with the root vertices of selected sawtooth elements of bed knife 8 and also with the root vertices of circumferentially spaced counterpart sawteeth of bed knife 9 and, typi cally, the guide members can be spaced laterally, one from another, two pitch dimensions of the sawteeth of the two bed knives. It will be understood that guides 10 can vary in number with the stiffness of the polymeric material being shredded, thick stiff polymer segments requiring less support, and therefore fewer guides 10, than thin flimsy segments.

As indicated in FIG. 2 guide members 10 are retained in exact alignment with the sawteeth root vertices by press fit attachment within machined slots provided on the trailing side of bed knife 8 and the leading side of the bed knife 9.

Referring to FIGS. 5 and 6, the upper edges of guides 10 are all beveled leftwards the same amounts to present downwardly inclined carnming surfaces 24, which bias the cut-away segments 35 to the left exactly onehalf of a sawtooth (or segment) pitch during the transit of the segments from bed knife 8 to bed knife 9 as shown by the successive positions taken by each segment, denoted in order, 35a-35d, FIG. 6.

Typically, rotary cutter l is operated at about l,l60 yards per minute tooth tip speed. At such high speed, substantial windage is generated, which can override the suction purge applied via draw-off funnel 12. Under these conditions, minute particles and dust debris would be expelled from entrance slot 6 into the web manufacturing area. Moreover, the high speed shredding action induces a violent flutter and uncontrollable feeding of the incoming web, severely reducing shredding efficiency.

To avoid these difficulties, it is preferred to install a debris-retaining auxiliary 7 such as detailed in side elevation section in FIG. 2.

Auxiliary 7 comprises a slightly inclined horizontally disposed retractable bristle brush 25 which extends across the full width of entrance slot 6 and is secured to holder 26 mounted within box housing 30. Holder 26 is provided with gear racks 27a, 27b at the ends which operatively engage with gears 28a, 28b, respectively, pinned to a common shaft 29 journaled in uprights on frame 3, not detailed.

A motor drive (not shown) is coupled to shaft 29 and provides the means for retracting and lowering brush 25 against the upper surface of web 40 as it is fed into the shredder, box housing 30 being moved simulta neously as denoted in broken line representation for the elevated position by reference numeral 31. During operation, brush 25 is lowered to a position contacting the web, thereby steadying its feed to the cutter and, at the same time, barring dust and particle escape out of slot 6.

Elevation of brush 25 and its housing 30 permits greater clearance for initial insertion of the end of web 40, and also facilitates repairs and maintenance.

Directly opposite brush 25 there is provided a rectangular cross-section air supply plenum chamber 33 which is supplied with pressurized air via line 34 leading to an air blower, not shown. The upper wall of chamber 33 serves as the support surface for the polymeric web input, and there is provided an air supply slot orifice 32 here extending the till width of slot 6 and aligned generally parallel to the direction of feed of the incoming web. This air clears out any out fragments from under web 40 and, at the same time, supplies air insuring a good volume sweep through housing 2.

Referring to FIG. 6, in operation a thin segment 35 is cut from web 40 each time a rotating knife 20 sweeps past the primary bed knife 8. These segments are rotated about their longitudinal axes approximately in a counter-clockwise direction as viewed in FIG. 2 as they are impelled along by the rotation of knives 20. Simultaneously, howevery, the force of gravity, aided by the centrifugal force of knives 20, displaces the segments downwardly along carnming surfaces 24, so that there occurs leftward displacement of each segment a distance of exactly one-half pitch dimension, as will be understood by reference to the successive positions 35a-35d taken by each segment in the sequence extending from bed knife 8 to bed knife 9, FIG. 6.

It will be seen that the point of contact 36 of each cut-out segment 35 with guide members 10 advances up each adjacent serration leg through the successive positions 36', 36 and 36", until the adjacent vertex is squarely biased across the root portion of secondary bed knife 9 on arrival there. At this point the sweep of the knives 20 past the saw teeth of bed knife 9 effects uniform simultaneous transverse severing across the full length of each segment 35 presented in turn. As seen in FIG. 6, the transverse cuts effected produce diamond patterns, denoted at 38, and adjacent chevrons 39, both of which are relatively small in size and this immediately swept downwardly through inlet 11 into draw-off funnel 12 and thence to remote storage via waste conveyor conduit 13.

The shredding apparatus of this invention has a very high shredding capability, webs 65 inch wide in the range of 0.0040.035 inch thick having been shredded at a web feed rate of 225 ftJmin.

What is claimed is:

1. Apparatus for shredding a polymeric web comprising, in combination, a power-driven rotary cutter provided on the periphery with at least one radially disposed sawtooth cutter blade aligned substantially coparallel with the longitudinal axis of said cutter, first and second stationary sawtooth bed knives disposed in interdigitating relationship with respect to said sawtooth cutter blade of said rotary cutter, said second stationary sawtooth bed knife being spaced away from said first stationary sawtooth bed knife in the direction of rotation of said rotary cutter a sufficient distance to permit positioning of individual polymeric segments cut away from said web at said first stationary sawtooth bed knife under the force of gravity and displacement by said rotary cutter during said rotation to a location relative to said second stationary sawtooth bed knife effecting transverse cutting of said polymeric segments during the interdigitating sweep of said sawtooth cutter blade of said rotary cutter past the sawteeth of said second stationary sawtooth bed knife, guide means disposed between said first and said second stationary sawtooth bed knives positively guiding said polymeric segments to said position for said transverse cutting of said segments, and means removing cut pieces of said polymeric segments from the vicinity of said second stationary sawtooth bed knive.

2. Apparatus for shredding a polymeric web according to claim 1 wherein said first stationary sawtooth bed knife is disposed in a substantially horizontal plane below the longitudinal axis of said rotary cutter and said second stationary sawtooth bed knife is disposed at a generally lower level than said first stationary sawtooth bed knife and at an angle with respect to said first stationary sawtooth bed knife greater than about and at a spacing in said direction of rotation of said rotary cutter from said first stationary sawtooth bed knife greater than about 60 of the circumference of said rotary cutter.

3. Apparatus for shredding a polymeric web according to claim 2 wherein said guide means disposed between said first and said second stationary sawtooth bed knives comprise a plurality of arcuate members disposed approximately equidistant radially with respect to said rotary cutter, said arcuate members being provided along the inboard edges with camming surfaces polymeric said ploymeric segments approximately one half pitch laterally in the course of transit of each said polymeric segment from said first stationary sawtooth bed knife to said second stationary sawtooth bed knife.

4. Apparatus for shredding a polymeric web according to claim 1 wherein said power-driven rotary cutter is provided on the periphery with a plurality of radially disposed sawtooth cutter blades aligned substantially co-parallel with the longitudinal axis of said cutter and spaced apart substantially equiangularly with respect to said rotary cutter.

5. Apparatus for shredding a polymeric web according to claim 1 wherein said power-driven rotary cutter and said first and second stationary sawtooth bed knives are disposed within an enclosed housing and said means removing said cut pieces of said polymeric segments from the vicinity of said second stationary sawtooth bed knife is an air sweep directed generally away from said rotary cutter.

6. Apparatus for shredding a polymeric web according to claim 5 provided with a polymeric web feed-in slot in general prolongation with said first stationary sawtooth bed knife, retractable close-off means biased across said web feed-in slot at a clearance admitting said polymeric web into said housing but barring escape of said cut pieces of said polymeric segments out of said enclosed housing, and pressurized air supply means introducing air under pressure directed toward said rotary cutter from the bottom side of said web feed-in slot.

=l= 0 l l 1333 33 UNITED STATES PATENT OFFICE CERTIFICATE OF (JORRECTION Patent No. 7 5 D d October 2, 19?} Inventor 5) DAVID LOUIS FRANTZ It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

3' Column 6, line 18, the word "polymeric" should read displacing the Word "ployme'ric" should read I polymeric Signed and sealed this 12th day of February 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. Attesting Officer C. MARSHALL DANN Commissioner of Patents 

1. Apparatus for shredding a polymeric web comprising, in combination, a power-driven rotary cutter provided on the periphery with at least one radially disposed sawtooth cutter blade aligned substantially co-parallel with the longitudinal axis of said cutter, first and second stationary sawtooth bed knives disposed in interdigitating relationship with respect to said saw-tooth cutter blade of said rotary cutter, said second stationary sawtooth bed knife beiNg spaced away from said first stationary sawtooth bed knife in the direction of rotation of said rotary cutter a sufficient distance to permit positioning of individual polymeric segments cut away from said web at said first stationary sawtooth bed knife under the force of gravity and displacement by said rotary cutter during said rotation to a location relative to said second stationary sawtooth bed knife effecting transverse cutting of said polymeric segments during the interdigitating sweep of said sawtooth cutter blade of said rotary cutter past the sawteeth of said second stationary sawtooth bed knife, guide means disposed between said first and said second stationary sawtooth bed knives positively guiding said polymeric segments to said position for said transverse cutting of said segments, and means removing cut pieces of said polymeric segments from the vicinity of said second stationary sawtooth bed knive.
 2. Apparatus for shredding a polymeric web according to claim 1 wherein said first stationary sawtooth bed knife is disposed in a substantially horizontal plane below the longitudinal axis of said rotary cutter and said second stationary sawtooth bed knife is disposed at a generally lower level than said first stationary sawtooth bed knife and at an angle with respect to said first stationary sawtooth bed knife greater than about 90and at a spacing in said direction of rotation of said rotary cutter from said first stationary sawtooth bed knife greater than about 60* of the circumference of said rotary cutter.
 3. Apparatus for shredding a polymeric web according to claim 2 wherein said guide means disposed between said first and said second stationary sawtooth bed knives comprise a plurality of arcuate members disposed approximately equidistant radially with respect to said rotary cutter, said arcuate members being provided along the inboard edges with camming surfaces polymeric said ploymeric segments approximately one half pitch laterally in the course of transit of each said polymeric segment from said first stationary sawtooth bed knife to said second stationary sawtooth bed knife.
 4. Apparatus for shredding a polymeric web according to claim 1 wherein said power-driven rotary cutter is provided on the periphery with a plurality of radially disposed sawtooth cutter blades aligned substantially co-parallel with the longitudinal axis of said cutter and spaced apart substantially equiangularly with respect to said rotary cutter.
 5. Apparatus for shredding a polymeric web according to claim 1 wherein said power-driven rotary cutter and said first and second stationary sawtooth bed knives are disposed within an enclosed housing and said means removing said cut pieces of said polymeric segments from the vicinity of said second stationary sawtooth bed knife is an air sweep directed generally away from said rotary cutter.
 6. Apparatus for shredding a polymeric web according to claim 5 provided with a polymeric web feed-in slot in general prolongation with said first stationary sawtooth bed knife, retractable close-off means biased across said web feed-in slot at a clearance admitting said polymeric web into said housing but barring escape of said cut pieces of said polymeric segments out of said enclosed housing, and pressurized air supply means introducing air under pressure directed toward said rotary cutter from the bottom side of said web feed-in slot. 